To carry out welding of particularly thin-walled products with large cross-sections, the joint edges of the products must be completely congruent with regard both to thickness and to circumference, taking account of concentricity and centering precision of the parts to be welded.
It is likewise generally known that, when full fusion welding jackets or plates, a biaxial stress state of the metal arises in the welding zone, which is the consequence of displacement of the edges to be welded on heating by the moving heat source. In the case of plates which are full fusion welded without an interspace, the edges cannot move unhindered in front of the heat source, and elastic compression of the metal takes place within them, drooping plastic deformation of the metal occurring. During passage of the heat source a comparatively narrow zone of the metal is affected by the displacement, namely that zone heated to an elevated temperature. Reinforcement of the plates therefore exerts virtually no influence on the transverse movement of the edges during welding. On welding cylindrical jackets, apart from the plastic deformation involving axial droop of the metal, a change in the diameter thereof also takes place, which leads to axially symmetrical deformation of the sections to be welded.
Deformation due to uneven heating over the width and length of the weld seam by nature constitutes bending strain. Flexure takes place as a result of the fact that the heated side broadens, while the cold side works against this broadening. To the extent that the width of the heated zone reduces at constant heat source power, the deformations caused by rotation of the sections also reduce. With very narrow heating zones, it may so happen that the jackets to be welded do not exhibit any significant angular deformations.
As a result of the above explanations, the task arises of selecting the optimum dimensions for the zones from which it is necessary to dissipate the heat, and also of producing designs for devices for achieving this object, in order to prevent bulging during welding and to reduce the residual stresses in the structures to be welded.
Methods are known for welding tubes and containers using devices which bring about centering relative to the external diameter (B. E. Paton, Technologija elektri□eskoj svarki metallov i splavov plavneniem, Moscow, Ma{hacek over (s)}inostroenie, 1974.)
The solutions according to the stated methods using known devices cannot in practice be used when welding thin-walled structures.
As the closest prior art with regard to the object of the invention and the method of achieving the object, a device was selected which comprises cylindrical alignment bushes with a fastening unit that allows centering of tubes on welding and which is known from RU 2 303739 C1.
A disadvantage of this solution is that it cannot be applied in the case of welding thin-walled jacket structures.